Objective To analyze the clinical distribution characteristics and changing trend of postoperative pneumonia (POP), and provide basis for further monitoring and management of POP. Methods Clinical data of POP patients in the First Affiliated Hospital with Nanjing Medical University from 2014-2023 were collected. The incidence of POP, the changing trend of proportion of ventilator-associated pneumonia (VAP), the occurrence time, pathogen distribution, and incidence of POP in various departments were analyzed retrospectively. Results From 2014 to 2023, a total of 653 609 patients in the hospital received surgery, with 676 245 times of operations, out of which 2 934 cases had POP, and the incidence of POP was 0.43%. The average age of POP patients was (59.76±16.53) years old, with 68.58% being male. The incidence of POP decreased from 2.00% in 2014 to 0.10% in 2023, and the proportion of VAP increased from 9.92% in 2014 to 99.10% in 2023, with statistically significant differences (all P<0.001). POP occurred within 7, 10, and 30 days after surgery accounted for 65.81%, 78.80%, and 95.64%, respectively. The top three departments with the highest incidences were cardiovascular surgery (5.277%), neurosurgery (2.114%), and thoracic surgery (1.130%). The main pathogen of infection was Gram-negative bacteria (77.58%). Conclusion The incidence of POP shows a downward trend. VAP patients should be the focus of follow-up improvement work. Departments of cardiovascular surgery, neurosurgery, and thoracic surgery are the key departments of POP, and 10 days after surgery should be the critical period of POP.